From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8258B606A31C for ; Thu, 29 Oct 2026 10:44:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ZledwiEK Received: by kanga.kvack.org (Postfix) id E6FBD6B05C1; Thu, 29 Oct 2026 06:44:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E472D6B05C2; Thu, 29 Oct 2026 06:44:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D10736B05C3; Thu, 29 Oct 2026 06:44:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id A5EBE6B05C1 for ; Thu, 29 Oct 2026 06:44:56 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 8F67080358 for ; Thu, 29 Oct 2026 10:44:54 +0000 (UTC) X-FDA: 85375330908.21.921AC8F Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf13.hostedemail.com (Postfix) with ESMTP id BFB8C2000C for ; Thu, 29 Oct 2026 10:44:52 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ZledwiEK; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf13.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793270692; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Ut7Dt82wxOXFB5jpdWIg+mDSfYAPLIzuxLMN5AZIwOs=; b=E7uEntG0s3SnRpw2DQdDNRXywQFw++jJaVtxIwJKGXvizvH47+8jn2xYY/8h1N2dgRlowh 6aQwzpDkvknycUWGZ2VKhsUnwQYE8uQZSr2DonPh15fjfNJbX0jzhqHtSzaZbjoLD/Ci8W 0OlLxVBXzfDK16DXAiIWwK+mAhLYPPQ= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ZledwiEK; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf13.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793270692; b=IM0wq4GEFrvqv2/AKIoQfTV7iaySc95KDmWWo87y34J+CJ9uMv++If6MUyF8wZ69qzypBj prL4cFJeLLAXQOOXZCkQ8yLaS3LlE4DVXzYG7KpRlpjN41aOLTr0+EmoEYbjVakT3M6L9o mCKT2woLzUHACtigc5vSmOobTuM/GhA= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 1CD04434AA; Thu, 29 Oct 2026 10:44:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B7281F01829; Thu, 29 Oct 2026 10:44:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793270692; bh=Ut7Dt82wxOXFB5jpdWIg+mDSfYAPLIzuxLMN5AZIwOs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ZledwiEKv+uPF8i5NY45vGiD9j7X//bQqac/nqFiP/bjk8eAu60EZXg9cGveJxx2x sqH8sWSAMIZChXFdncdC782UEPe/hNM4cIhY8mSELF5CNn2U0VOQXTtDq9z1bnEqP/ i3WR0JXckZJkd87I42c6K0lYzSRD/5MBe2EnknXfvjJgEHh6YqQcKAGnmG9RHfuAsx HZ/73S5FHenZvLZHcZb9zXlrfUObqrD1jdyOfehQCQZImtNA6/ANIFtbAcCxzSTtI0 Sqfy7iY8MQ5kjD2IofCUOfyRiEQcS/Qd/ZJ43Fjtu0YrHEIrLDVSTlD2o5lSvdjTww x0RkZ1QsCM92Q== Message-ID: Date: Thu, 29 Oct 2026 11:44:46 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] RDMA/uverbs: Don't return the shared zero page from rdma_umap_fault() To: Zi Yan Cc: Jason Gunthorpe , Leon Romanovsky , linux-mm@kvack.org, Lorenzo Stoakes , Lance Yang , Kiryl Shutsemau , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261025-fix-rdma_umap_fault-zero-page-v1-1-186255624f1f@nvidia.com> <78802ed9-9cc6-41c4-b131-7c7d38f7ff39@kernel.org> <829c448d-e6e2-4874-a166-7624e87489ef@kernel.org> <5E86E76B-F97A-4998-9EDB-8E450470FA4A@nvidia.com> <44a5aa3e-173c-41fd-bbb5-92ae9d1cdc8f@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: BFB8C2000C X-Rspam-User: X-Stat-Signature: x5wezem88ubdpe535d44y1h8n6n15g8g X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1793270692-488889 X-HE-Meta: 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 1jSC6yTc Tbd3Ev8QBOMzl1QKfEdX7KIuIlz3m/NeGrfPStrnbUuiwYAZensBpMDIfKE+oIEjA2JbCzfsLZRcc95KLIudLw68nLi+7GIyCHvk92JOipOFTM4F2m/CIrLFGuFA/HZJ1bXEs58rbRz9dumrJqnnfWuihtH89zGkSjsz5m4VyZva+/yvH+o0aIe4ue9842txz7FSiXYlaJ1FEYZ8gQN5RUsEFkg/Rwp7Mrthv3ctl9LY+jkpvOeWUBKGr8LVdd3XDiQ0oSsyiYVdefU7m0aONxYc7yh/MPevbJAcVpvQGBOnjYg10erjqV1aSNw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/29/26 03:00, Zi Yan wrote: > On 28 Oct 2026, at 16:34, David Hildenbrand (Arm) wrote: > >> On 10/28/26 18:49, Zi Yan wrote: >>> >>> >>> Not urgent. Like Jason said in another email, RDMA only runs on arch >>> with special PTE, so refcount, mapcount, rss are balanced. With DEBUG_VM, >>> zero_page checks in rmap will fire on the returned zero_page. >>> >>> >>> There is one wrinkle, it does not work on >>> s390 + mm_forbids_zeropage() == true, where zero page is not present, >>> and a private zero page is needed. >> >> Yes, see vm_mixed_zeropage_allowed() I added. >> >> In a VM_PFNMAP it doesn't matter. It's only a problem if we can GUP involved >> IIRC, and VM_PFNMAP just disallows it entirely. >> >> Similar for s390, it doesn't support any form of memory deduplication (incl. >> shared zeropage) for some KVM use cases. IIRC, PFNMAP does not really apply there. > > Got it. It is then all clear to modify vmf_insert_pfn_prot() to support > zeropage for VM_PFNMAP (no huge zeropage support will be added). > >> >> (have to make sure that gup-fast doesn't try pinning the shared zeropage) > > With special pte, GUP-fast bails out on the PTE. Without special pte, > gup_fast_pte_range() simply returns 0. Then GUP slow rejects VM_PFNMAP. > >> >> (of course, the shared zeropage must never get mapped writable) > > vmf_insert_pfn_prot() will only accept a shared zeropage on a VMA if the > VMA has neither VM_WRITE nor VM_MAYWRITE. It should prevent the VMA > becoming writable. Also it will ensure the result PTE is not writable. > > As we discussed on IRC, VM_WARN_ON_ONCE_VMA(vma->vm_flags & VM_PFNMAP, vma) > will be added after __do_fault() to enforce no page is returned > from ->fault(). > > Since it is not urgent, I will probably send V2 after rc1 is out. > Thank you for all the info. Thanks for handling this! -- Cheers, David